A soft, supple and flexible skin has a marked cosmetic appeal and is an attribute of normal functioning epidermis. As human skin ages with advancing years, the epidermis can become folded, ridged or furrowed to form wrinkles. These signal loss of youthful appearance and herald the transition to old age. Exposure to excessive doses of sunlight accelerates the transition process. The outer layer of the epidermis (the stratum corneum) can also become dry and flaky following exposure to cold weather or excessive contact with detergents or solvents. Loss of skin moisture thereby results, and the skin begins to lose the soft, supple and flexible characteristics.
Emollients such as fats, phospholipids and sterols have in the past been used to soften wrinkled or dry skin. These emollients have proven to be only partially effective in improving the condition of the skin.
Carboxylic acids have been employed successfully in improving the quality of human skin, by moisturizing the skin and exfoliating dead skin cells from the epidermal layer. In particular, .alpha.-hydroxy carboxylic acids (".alpha.-hydroxy acids"), .beta.-hydroxy carboxylic acids (".beta.-hydroxy acids") and carboxylic acids including an .alpha. or .beta. keto group ("keto acids") have proven highly effective therapeutically. Compositions and methods employing .alpha.-hydroxy acids are disclosed in a large number of patents. U.S. Pat. No. 4,105,782, to Yu et al., discloses the use of amines or ammonium salts of .alpha.-hydroxy carboxylic acids in the treatment of acne or dandruff. U.S. Pat. Nos. 4,021,572, 4,105,783, 4,197,316 and 4,363,815, to Yu et al., teach the use of free .alpha.- and .beta.-hydroxy acids and keto acids, and also peroxides, amides, lactones, anhydrides, esters, and salts of such acids, for the treatment of numerous skin conditions, including dry skin, ichthyosis, keratoses and hyperkeratoses, psoriasis, eczema, etc. U.S. Pat. No. 4,234,599, to Van Scott et al., reveal the use of .alpha.-hydroxy carboxylic acids, their esters or amine salts in the treatment of keratoses. U.S. Pat. No. 4,424,234, to Alderson et al., teaches skin treatment compositions incorporating .alpha.-hydroxycaproic acid and .alpha.-hydroxycaprylic acid or mixtures thereof in acidic compositions (pH typically from 2 to 4). U.S. Pat. No. 5,091,171, to Yu et al., describes the use of such compounds against age spots, wrinkles and aging related skin changes.
Although compositions including hydroxy and/or keto acids have proven very successful in treating many skin conditions, they are not without certain problems. For example, exposure of new or previously untreated skin to .alpha.-hydroxy acid compositions can cause irritation, particularly if the treatment is carried out too quickly. U.S. Pat. No. 5,382,432, to McCook et al., addressed this problem by using a series of compositions having increasing concentrations of .alpha.- or .beta.-hydroxy acids over time, in order to allow the skin of the user to grow accustomed to the irritation produced by the acids.
The known skin conditioning compositions which include hydroxy or keto acids have typically been prepared in the form of lotions, sprays, creams, molded sticks, and the like, and have been packaged and dispensed from conventional tubes, lidded jars, aerosol or pump stray containers, stick applicators, etc. With the development of the soft gelatin capsule, or softgel, an alternative form of dispensing and applying such skin conditioning compositions has become available. Encapsulation of a skin conditioning composition in a softgel offers numerous advantages. For example, no additional packaging would be needed for the filled softgels. The compositions could be prepared in pre-measured quantities effective to moisturize the skin of the user, thus minimizing waste of the compositions.
For practicable encapsulation within a softgel, however, the skin conditioning composition must be compatible with the softgel. In particular, the composition must be formulated such that it can be stably encapsulated in the softgel shell without dissolving the softgel. The composition should be formulated such that it is stable in encapsulated form for extended periods of time at room temperature.
A need exists for skin conditioning compositions including hydroxy and/or keto acids that are compatible with a softgel shell and can be encapsulated stably in a softgel. Desirably, the compositions should be gentle to the skin as well.